Ten subjects with moderate to advanced HIV infection who are about to begin anti-retroviral therapy for the first time or who are going to have a change their anti-retroviral drug regimen. Each will undergo lumbar puncture before initiating or changing therapy. Plasma specimens will be obtained. HIV RNA levels will be measured. Levels will be correlated with the extent of disease as judged by clinical examination. Change in RNA levels will also be correlated with known penetration of the drugs being used into the cerebrospinal fluid.